This invention relates to an internal combustion engine and more particularly to an improved operational control system for a two-cycle, direct cylinder injected, internal combustion engine.
As is well know, two-cycle internal combustion engines have a number of advantages. One of these advantages is that this type of engine provides a relatively high specific output in relation to its displacement. This is a result of the engine firing every crankshaft revolution, as opposed to every other crankshaft revolution, as with four-cycle engines.
Also, two-cycle engines generally are of the ported type, and hence, do not have the complicated valve trains and valve driving mechanisms associated with four-cycle engines. The fact that the scavenging cycle takes place at the same time as the exhaust cycle, however, gives rise to certain problems in connection with effective exhaust emission control.
In order to improve engine performance, it has been proposed to employ a direct cylinder injection system for two-cycle engines. With such a system, it is possible to obtain better control of the fuel-air ratio in the combustion chamber. However, the ported nature of the engine gives rise to the possibility that the direct spray of fuel into the combustion chamber may result in some of the fuel passing out of the exhaust port during running conditions, and particularly when large durations of fuel injection are required.
Also, it has been proposed to mount the fuel injector for a two-cycle engine in a location where it will be shielded by the piston during a portion of the combustion cycle. This protects the injector from contamination, and yet permits the use of lower cost fuel injectors than those that are exposed to the maximum combustion pressure and temperature. However, this shrouding of the fuel injector further restricts the time at which fuel can be injected, and thus gives rise to the aforenoted problems.
In accordance with an important feature of the invention, it is proposed to embody a system that employs an exhaust control valve which controls the effective cross-sectional area of the exhaust port, and can cooperate to reduce the likelihood of unburned fuel from passing out of the exhaust port. By controlling the position of the exhaust control valve in response to running conditions such as speed and/or load, exhaust emission control can be facilitated.
It is possible to provide a map that will show the correct exhaust control valve position under a wide variety of engine speed and loads, and thus permits the desired results to be achieved. However, there are some conditions where the position of the exhaust control valve cannot or should not be dictated by either or both of load and/or speed.
It is, therefore, a principal object of this invention to provide an improved operating control system for a two-cycle, direct injected engine.
It is a further object of this invention to provide an exhaust control system and method for operating it for such engines, which is responsive to a wide variety of engine running conditions so as to improve performance under all conditions.
Low speed and low load conditions are one condition when the control of the effective area of the exhaust passage can be significant. Under these conditions, there is a likelihood of irregular combustion due to the low speed. That is, at low speed operation there is relatively sluggish movement of the scavenging gases in the combustion chamber. This coupled with the overlap in the porting can cause exhaust gases to flow back into the combustion chamber and decrease the effective fuel-air ratio. This also causes poor flame propagation. Thus, by restricting the exhaust flow area under this condition, it is then possible to improve combustion stability.
However, when the engine is accelerated rapidly from this condition, the closed position of the exhaust valve may cause sluggish flow out of the exhaust system and retard rapid acceleration. Furthermore, this can cause rise in temperature in the combustion chamber.
On the other hand, if the engine is decelerated rapidly, then also the discharge of exhaust gases may be restricted, and high temperatures and engine stall are possible.
It is, therefore, a still further object of this invention to provide an improved exhaust control system for a two-cycle, direct injected engine that improves the performance under sudden changes in engine speed, such as rapid acceleration or deceleration.
Another condition when the positioning of the exhaust control valve should not necessarily be dictated from engine speed and/or engine load is during starting and initial warm-up. Again, because of the poor scavenging that may result at low speeds and the likelihood that exhaust gases can enter the combustion chamber, idling and low speed operation can be improved by restricting the exhaust gas flow.
However, the basic same operating condition of the engine, i.e., low speed and low load, also occurs during cranking for starting. Restricting the exhaust control valve under this time can cause poor start-up performance. It is normally the practice to enrich the fuel amount when the engine is started, and this results in an overly rich mixture, since the intake air does not correspond to the increased amount of fuel.
It is, therefore, a still further object of this invention to provide an improved exhaust control arrangement for a two-cycle, direct injection engine, wherein start-up performance is facilitated.
In addition to the initial starting of the engine, it is also necessary to ensure that once the engine is started, it can warm up rapidly so that it will reach its operating temperature sooner and improve the efficiency of the engine. This also is a running condition when the position of the exhaust control valve should not be controlled only by engine load or speed.
It is, therefore, a still further object of this invention to provide an engine warm-up control arrangement for controlling the exhaust gas discharge of a two-cycle, direct injection-type of engine.